In early 1779 Father Pierre Gibault, a supporter of the American cause, found himself hiding on an island in the Mississippi River. Both ice and the lack of a formal alliance between Spain and the United States blocked his path to the Spanish west bank, while a British military expedition prevented him from returning to the east bank. As the French-Canadian priest struggled to keep warm he probably pondered the delicacy of his position: surrounded by enemies, unreliable allies, and a host of powerful Native groups he did not understand. In the years before, during, and after the American Revolution, the Mississippi River served as both a highway and a border between empires. Trade, diplomacy, and war all depended on the waters of the river. Other than the Appalachian Mountains, no other physical feature in North America figured as prominently as the Mississippi River. The waters tumbled settlers, soldiers, adventurers, and merchants together along the banks in a complex mixture of cultures. The geographically dictated blending of cultures, the limited number of European settlers residing on the banks of the Mississippi River, and the overwhelming military and political superiority of Native groups who made the region their home, created a unique European middle ground in the heart of the continent. Living under the hammer of a Native dominance that never fell, European and American settlers and soldiers in the region picked their steps carefully. Religious and political concerns paled in comparison to the practical matter of survival. Europeans and Americans on the banks of the river shared a unique political malleability born of vulnerability. This malleability made the western frontier of the American Revolution a peculiar landscape into which, mere handfuls of men were able to tip the balance of power toward the Spanish and American cause.